The present invention relates to a liquid injecting apparatus that jets liquid from a nozzle to a target.
Inkjet printers are widely known as liquid injecting apparatuses for injecting liquid from a nozzle of a recording head onto target. For example, a serial printing type inkjet printer includes an inkjet recording head (hereinafter referred to as recording head), which is mounted on a carriage and reciprocated in a main scanning direction, and paper feeding means, which feeds sheets of recording paper in a direction perpendicular to the main scanning direction. The recording head jets ink droplets based on printing data, thereby executes printing on the recording paper. Many of inkjet printers that are mainly used at home have ink cartridges for supplying ink to the recording head. Ink cartridges are detachably mounted on the carriage mounting the recording head.
A typical recording head used in inkjet printers has a pressurizing chamber. Ink is pressurized in the pressurizing chamber and discharged through nozzle openings as ink droplets to recording paper. Ink solvent (for example, water) evaporates from the nozzle openings. This increases the viscosity of the ink and solidifies the ink. Also, dust collected on the nozzle opening and bubbles trapped in the ink hinder normal discharge of ink droplets. Abnormal ink discharge results in poor printing.
Therefore, this type of inkjet printer has capping means and wiping means. The capping means seals the surface of the recording head on which the nozzles are located when printing is not being performed. The wiping means wipes and cleans the nozzle surface of the recording head as necessary. When the inkjet printer is not printing, the capping means functions as a cover for preventing ink at the nozzle openings of the recording head from being dried. The capping means also has maintenance function. Specifically, when the nozzle openings are clogged, the capping means seals the nozzle surface, so that the negative pressure of a suction pump acts on the nozzle openings. This draws ink from the nozzle openings and opens the nozzle openings.
The forcible suction of ink to get rid of clogging of the recording head is referred to cleaning operation. For example, when an inkjet printer is used after a long interval, the cleaning operation is automatically executed. Also, when a user discovers poor printing results and turns a cleaning switch, the cleaning operation is executed.
In the maintenance function by the cleaning operation, the nozzle surface of the recording head is sucked using the capping means. Thus, even if the negative pressure is removed after the suction, a slight vacuum pressure remains in the recording head. Further, since there are bubbles in the ink discharged to the capping means, bubbles are drawn into the nozzle openings. Therefore, even if the cleaning operation is executed, the printing quality deteriorates. In other words, the reliability of the cleaning operation is lowered.
In the valve unit of the above inkjet printer, bubbles caught in ink supplied from the ink cartridge, bubbles remained after the initial charging, and bubbles drawn through the nozzle openings of the recording head reside in the pressurizing chambers. The residing bubbles lower the filling factor of ink in the pressurizing chamber. The bubbles in the pressurizing chamber flow out during printing, which degrades the printing quality.